The growth of optical networks for voice and data communication has created a demand for high data-rate information-transfer capabilities. To enable such transfer capabilities, dense wavelength division multiplexing (DWDM) technology has been developed which allows transfer of multiple wavelength light beams over a single optical fiber enabling data transfer rates up to 100 Gb/s. High-speed switching and routing devices are core elements of the optical networks and allow dynamic control of the data traveling over the optical network. High data-transmission rates impose significant demands on the functionality of the switching devices.
Optical switching devices are commonly used in networks to redirect signals. For example, an N-by-M optical switch accepts as many as N input signals at N input fibers and diverts the output, and thus switching signals, among M output fibers. A particularly useful optical switch is a one-by-N switch (or “1×N optical switch”), that accepts a single signal at an input fiber and switches the signal to one of N output fibers. One-by-N optical switches are used, for example, to reconfigure networks due to lost connections, and monitoring and provisioning to ensure high quality connections.
While the use of optical switches has the potential for making optical networks fast and reliable, it has proven difficult to produce cost effective and dependable optical switches. Many types of optical switches have been proposed, including different schemes for switching an optical input to a particular optical output. Optical switches include electrically-based optical switches and mechanically-based optical switches. Electrically-based optical switches convert signal-containing light (or “optical signals”) into electrical signals, re-route the electrical signals, and then convert the electrical signals back into light signals. Mechanically-based optical switches direct light signals using movable mirrors. Both of these types of optical switches have problems that limit their usefulness. Electrically-based optical switches involve conversion steps that make these switches expensive and slow. Mechanically-based optical switches have additional problems that limit their use in high speed systems, including reliability problems due to the large number of small movable mirrors, and switching times that are limited by the physical movement of mirrors.
Another type of optical switch is and all-optical switch having no moving parts and not involving conversion of the light signal to another form for switching. In all-optical switches, light signals are directed within optical materials having optical properties that can be modified.
One type of all-optical switch has a plurality of inputs and a plurality of outputs separated by a common waveguide. See, for example, commonly assigned U.S. Pat. No. 6,504,966 by Kato et al. (the “Kato patent”), and incorporated herein by reference. Switching is accomplished by the routing any one of the input light beams through the common waveguide to a desired output. Each switched signal is deflected at the input, to direct the input from an input fiber to the output, and at the output, to direct the output into an output fiber. While such devices provide for switching between a large number of inputs and outputs, the configuration results in optical losses that are greater than for other 1×N optical switches.
Another all-optical 1×N switch is assembled from multiple 1×2 all-optical switches to form a switch with a single input and a plurality of outputs, forming a 1×N switch from N−1, 1×2 optical switches. This type of optical switch has several problems. First, there is an insertion loss of the light signal with each pass through a light switch. Since the number of switches through which the light signal must pass increases with N, the loss also increases with N. Second, each of the N−1 switches has a given power requirement and has to be controlled in unison with the other switches. This type of switch thus presents electrical and control problems.
Therefore, it would be desirable to have a 1×N, all-optical switch for an optical communication system that overcomes the problems with prior optical switches and is faster, more reliable and less expensive to construct, and has lower insertion losses than current optical switches. It is also desirable for a switch to be rugged and compact.